The effect of oxalic acid on phenanthrene sorption was varied from that on pyrene sorption. 1.0 mg L^-1 of oxalic acid inhibited phenanthrene sorption, whereas 20, 50 and 100 mg L^-1 of oxalic acid enhanced the sorption. However, pyrene sorption onto biochar was all inhibited among different concentrations of oxalic acid. New functional groups and increased polarity were observed in the biochar coexisted with oxalic acid, moreover, a high concentration of oxalic acid led to an increased specific surface area of the biochar. These changed factors contributed to biochar sorption to phenanthrene, which was dominated by surface adsorption. Weakened aromaticity and increased release of dissolved organic carbon from biochar may have been the main reason for inhibited pyrene sorption onto biochar by oxalic acid. Therefore, this study suggested that root exudates could greatly influence the sorption behavior of biochar towards PAHs in soil rhizosphere, which deserves attention in agricultural systems.

草酸对菲吸附的影响不同于对pyr吸附的影响。1.0 mg L ^-1的草酸抑制了菲的吸附，而20、50和100 mg L ^-1草酸的增强吸附作用。但是，在不同浓度的草酸中，pyr吸附到生物炭上均被抑制。在与草酸共存的生物炭中观察到新的官能团和增加的极性，此外，高浓度的草酸导致生物炭的比表面积增加。这些变化的因素促成了生物炭对菲的吸附，菲主要由表面吸附。芳香性减弱和从生物碳中溶解的有机碳的释放增加可能是草酸抑制pyr吸附到生物碳上的主要原因。因此，这项研究表明，根系分泌物可能极大地影响生物炭在土壤根际中对PAHs的吸附行为，这在农业系统中值得关注。